Methods of reducing the stacking height of containers, lids, and bases

ABSTRACT

A method for forming a reduced-height stack of containers wherein the containers stacked contain at least one undercut and at least one undercut receiving structure. The first container having an undercut at a first position and an undercut receiving structure at a second position. The second container having an undercut at a third position and an undercut receiving structure at a fourth position. The containers may be arranged so that the at least one undercut of the first container at the first position aligns with and fits into the at least one undercut receiving structure at the fourth position of the second container below the first container in the stack.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 60/617,333, entitled “Methods of Reducing theStacking Height of Containers, Lids, and Bases” filed on Oct. 12, 2004,which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the packaging industry. Moreparticularly, the present invention relates to reducing the stackingheight of a stack of containers, lids, or bases.

BACKGROUND OF THE INVENTION

The packaging industry has produced a number of containers, lids, andbases to be used in applications such as egg cartons, carry-outcontainers, fruit trays, and other container types. These containers,lids, and bases are typically transported from a manufacturer to anentity that utilizes a container, lid, or base. The containers oftenhave locking mechanisms between its bases and lids. A container that isnot securely closed could open inadvertently and spill the contents ofthe container. Typically this locking mechanism is controls the designof the stack height. These containers, lids, and bases are oftentransported by being stacked inside boxes. The size of thesetransportation boxes is often referred to as the cube of the outerpackaging.

Referring now to prior art FIG. 1, a portion of a stack 30 that includesa plurality of containers 10 is shown. The distance indicated by arrow Ais the stack height between two containers. The term “stack height” asused in this application means the distance between identical featuresof adjacent containers in a stack. It can be observed in prior art FIG.1 that the stack height A is governed by a lead-in surface 18 of thelocking mechanism of the top container of the stack 30 resting on anundercut rim 16 of the locking mechanism of the bottom container of thestack 30.

Similarly, in prior art FIG. 2 a portion of a stack 40 that includes aplurality of containers 20 is shown. The distance indicated by an arrowB is the stack height between two containers. The stack height B ofprior art FIG. 2 is driven by an undercut rim 26 of the lockingmechanism of the first container resting on a lead-in surface 28 of thelocking mechanism of the second container in the stack 40.

A greater stack height results in a larger cube for the transportationboxes. A typical stack may include several hundred or even severalthousand containers, lids, bases, and combinations thereof. Having aninefficient stacking of containers, lids, and bases is costly because ofthe higher transportation costs involved. Additionally, potentialstorage costs may be incurred by the entities that use such itemsbecause of the inefficient stacking. Further, a large stack alsorequires additional store shelf-space, which increases the costassociated with marketing the containers. Such costs are ultimatelypassed onto the end user of the containers, lids, and bases.

A need therefore exists for a method to stack containers that results ina reduced stack height for an equal number of containers.

SUMMARY OF THE INVENTION

A method for forming a reduced-height stack of a plurality of containersprovides a first and second container. The first container has at leasta first undercut and at least one undercut receiving structure. The atleast a first undercut is located at a first position. The at least afirst undercut receiving structure is located at a second position. Thesecond container has at least a second undercut and at least oneundercut receiving structure. The at least a second undercut is locatedat a third position. The at least one undercut receiving structure is ata fourth position. The third position is a different location from thefirst position. The fourth position is a different location from thesecond position. The first and second containers are generally equal insize. The method arranges the first and second container to form a stackof a plurality of containers. The at least a first undercut of the firstcontainer aligns with and fits within the at least one undercutreceiving structure of the second container at the fourth position toreduce the stack height.

According to another method of the present invention, a method offorming a reduced-height stack of containers provides a mold base thatcomprises at least a first mold cavity that has a first design and asecond mold cavity that has a second design. The first design isdifferent from the second design. This method makes a first container inthe first mold cavity that has at least one undercut located at a firstposition and at least one undercut receiving structure located at asecond position. The method also makes a second container in the secondmold cavity that has at least one undercut located at a third positionand at least one undercut receiving structure located at a fourthposition. The third position is a different location than the firstposition. The fourth position is a different location than the thirdposition. This method removes the first and second containers from therespective first and second mold cavities. The method arranges the firstand second containers to form a two-container stack. The at least afirst undercut of the first container at the first position aligns withand fits within the at least one undercut receiving structure of thesecond container at the fourth position to reduce the height of thetwo-container stack.

According to a further method of the present invention, a method offorming a reduced-height stack of containers provides a mold base thatcomprises at least a first mold cavity and a second mold cavity. Thedesign of the first mold cavity is substantially identical to the designof the second mold cavity. The second mold cavity is rotated in the moldbase relative to the first mold cavity. This method makes a firstcontainer in the first mold cavity that has at least one undercutlocated at a first position and at least one undercut receivingstructure located at a second position. The method also makes a secondcontainer in the second mold cavity that has at least one undercutlocated at a third position and at least one undercut receivingstructure located at a fourth position. The third position is adifferent location than the first position. This method removes thefirst and second containers from the respective first and second moldcavities. The method arranges the first and second containers to form atwo-container stack. The at least one undercut of the first container atthe first position aligns with and fits within the undercut receivingstructure at the fourth position of the second container to reduce theheight of the two-container stack. The containers align without furtherrotation of the containers after they are removed from the moldcavities.

According to yet another method of the present invention, a method offorming two reduced-height stacks of containers provides a mold basethat comprises at least a first mold cavity, a second mold cavity, athird mold cavity, and a fourth mold cavity. The mold cavities arearranged in two rows and two columns. The first and second mold cavitiescomprise a first column of mold cavities. The third and fourth moldcavities comprise a second column of mold cavities. The design of thefirst mold cavity is different than the design of the second moldcavity. The design of the third mold cavity is different than the designof the fourth mold cavity. This method makes a first container in thefirst mold cavity that has at least one undercut located at a firstposition and at least one undercut receiving structure located at asecond position. The method also makes a second container in the secondmold cavity that has at least one undercut located at a third positionand at least one undercut receiving structure located at a fourthposition. The third position is a different location than the firstposition. A third container is made in the third mold cavity that has atleast at least one undercut located at a fifth position and at least oneundercut receiving structure located at a sixth position. A fourthcontainer is made in the fourth mold cavity that has at least at leastone undercut located at a seventh position and at least one undercutreceiving structure located at an eighth position. The fifth position isa different location than the seventh position. This method removes thefirst, second, third, and fourth containers from the respective first,second, third, and fourth mold cavities. The method arranges the firstand second containers to form a two-container stack. The at least oneundercut of the first container at the first position aligns with andfits within the undercut receiving structure at the fourth position ofthe second container to reduce the height of the two-container stack.The method arranges the third and fourth containers to form atwo-container stack. The at least one undercut of the third container atthe fifth position aligns with and fits within the undercut receivingstructure at the eighth position of the fourth container to reduce theheight of the two-container stack.

According to yet a further method, a method of forming tworeduced-height stacks of containers provides a mold base that comprisesat least a first mold cavity, a second mold cavity, a third mold cavity,and a fourth mold cavity. The mold cavities are arranged in two rows andtwo columns. The first and second mold cavities comprise a first columnof mold cavities. The third and fourth mold cavities comprise a secondcolumn of mold cavities. The design of the first mold cavity issubstantially identical to the design of the second mold cavity. Thesecond mold cavity is rotated within the mold base relative to the firstmold cavity. The design of the third mold cavity is substantiallyidentical to the design of the fourth mold cavity. The fourth moldcavity is rotated within the mold base relative to the third moldcavity. This method makes a first container in the first mold cavitythat has at least one undercut located at a first position and at leastone undercut receiving structure located at a second position. Themethod also makes a second container in the second mold cavity that hasat least one undercut located at a third position and at least oneundercut receiving structure located at a fourth position. The thirdposition is a different location than the first position. A thirdcontainer is made in the third mold cavity that has at least at leastone undercut located at a fifth position and at least one undercutreceiving structure located at a sixth position. A fourth container ismade in the fourth mold cavity that has at least at least one undercutlocated at a seventh position and at least one undercut receivingstructure located at an eighth position. The fifth position is adifferent location than the seventh position. This method removes thefirst, second, third, and fourth containers from the respective first,second, third, and fourth mold cavities. The method arranges the firstand second containers to form a two-container stack. The at least oneundercut of the first container at the first position aligns with andfits within the undercut receiving structure at the fourth position ofthe second container to reduce the height of the two-container stack.The first and second containers align without further rotation of thefirst and second containers after they are removed from the moldcavities. The method arranges the third and fourth containers to form atwo-container stack. The at least one undercut of the third container atthe fifth position aligns with and fits within the undercut receivingstructure at the eighth position of the fourth container to reduce theheight of the two-container stack. The third and fourth containers alignwithout further rotation of the third and fourth containers after theyare removed from the mold cavities.

According to still another method of the present invention, a method offorming a reduced-height stack of containers provides a mold base thatcomprises at least a first mold cavity and a second mold cavity. Thedesign of the first mold cavity is substantially identical to the designof the second mold cavity. This method makes a first container in thefirst mold cavity that has at least one undercut located at a firstposition and at least one undercut receiving structure located at asecond position. The method also makes a second container in the secondmold cavity that has at least one undercut located at a third positionand at least one undercut receiving structure located at a fourthposition. The third position is a different location than the firstposition. This method removes the first and second containers from therespective first and second mold cavities. At least one of thecontainers rotates after it is removed from the mold cavity. The methodarranges the first and second containers to form a two-container stack.The at least one undercut of the first container at the first positionaligns with and fits within the undercut receiving structure at thefourth position of the second container to reduce the height of thetwo-container stack.

According to one embodiment, a stack of containers comprises a firstcontainer and a second container. The first container comprises alocking mechanism. The first container locking mechanism includes atleast one undercut at a first position and at least one undercutreceiving structure at a second position. The second container comprisesa locking mechanism. The second container locking mechanism includes atleast one undercut at a third position and at least one undercutreceiving structure at a fourth position. The first and secondcontainers stack such that the at least one undercut at the firstposition is aligned with the at least one undercut receiving structureat the fourth position. The at least one undercut at the first positioncontacts the undercut receiving structure at the fourth position toreduce the height of the stack.

According to another embodiment, a stack of containers comprises a firstcontainer, a second container, a third container, a fourth container,and a fifth container. The first container comprises a lockingmechanism. The first container locking mechanism includes at least oneundercut at a first position and at least one undercut receivingstructure at a second position. The second container comprises a lockingmechanism. The second container locking mechanism includes at least oneundercut at the first position and at least one undercut receivingstructure at the second position. The third container comprises alocking mechanism. The third container locking mechanism includes atleast one undercut at a third position and at least one undercutreceiving structure at a fourth position. The fourth container comprisesa locking mechanism. The fourth container locking mechanism includes atleast one undercut at the first position and at least one undercutreceiving structure at the second position. The fifth containercomprises a locking mechanism. The fifth container locking mechanismincludes at least one undercut at the first position and at least oneundercut receiving structure at the second position. The secondcontainer aligns so that the at least one undercut at the first positionof the second container aligns with the at least one undercut at thefirst position of the first container. The third container aligns sothat the at least one undercut at the third position of the thirdcontainer aligns with and fits within the at least one undercutreceiving structure at the second position of the second container. Thefourth container aligns such that the at least one undercut at the firstposition of the fourth container aligns with and fits within the atleast one undercut receiving structure at the fourth position of thethird container. The fifth container aligns so that the at least oneundercut at the first position of the fifth container aligns with the atleast one undercut at the first position of the fourth container. Thestack height between the second, third, and fourth containers isminimized, and the total stack height is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the invention will become apparent upon reading thefollowing detailed description and upon reference to the drawings.

FIG. 1 is a sectional view of a prior art stack of containers;

FIG. 2 is a sectional view of another prior art stack of containers;

FIG. 3 is a sectional view of a locking mechanism for a containeraccording to one embodiment of the present invention;

FIG. 4 is a sectional view of a locking mechanism for a containeraccording to another embodiment of the present invention;

FIG. 5 a is a schematic view of a stack of two containers according toone embodiment of the present invention;

FIG. 5 b is a sectional view of a stack of two containers according toanother embodiment of the present invention;

FIG. 6 is a functional diagram of a mold base to be used to manufacturecontainers according to one embodiment of the present invention;

FIG. 7 is a functional diagram of a mold base to be used to manufacturecontainers according to another embodiment of the present invention;

FIG. 8 is a functional diagram of a mold base according to a furtherembodiment of the present invention;

FIG. 9 is a functional diagram of a mold base according to yet anotherembodiment of the present invention;

FIG. 10 is a sectional view of a stack of five containers according toyet another embodiment of the present invention; and

FIG. 11 is a functional diagram of a mold base according to yet afurther embodiment of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms disclosed but, on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Turning now to the drawings, FIG. 3 shows a locking mechanism 12 of acontainer 1 in the closed position. As used in this application the word“container” is defined herein as including, trays, lids, bases, bowls,combinations of lids and bases, combinations of lids and bowls, baseswith hinged lids, bowls with hinged lids, and combinations thereof. Thelocking mechanism 12 comprises a rim flange 14 and a correspondingundercut 16. The locking mechanism 12 functions by having the undercut16 go over the rim flange 14 so as to close the container 1. Theundercut 16 of FIG. 3 includes a lead-in surface 18.

Referring to FIG. 4, a locking mechanism 22 of a container 2 is shown inthe closed position according to another embodiment. The lockingmechanism 22 comprises a rim flange 24 and an undercut 26. The lockingmechanism 22 functions by having the rim flange 24 inserted into theundercut 26 so as to close the container 2. The undercut 26 has alead-in surface 28.

FIG. 5 a shows a schematic view of a two container stack 50 thatincludes a first container 52 and a second container 54. The first andsecond containers 52, 54 comprise respective locking mechanisms 22, 32that further comprise an undercut receiving structure 56 and an undercut58. The undercut receiving structure 56 is designed to allow theundercuts 58 of the locking mechanisms 22, 32 of the containers 52, 54in the stack 50 to be in closer proximity to each other, thus reducingstack height C (FIG. 5 b) of the stack 50. The undercut receivingstructures 56, as well as the undercuts 58, of the locking mechanisms22, 32 of the containers 52, 54 are offset relative to each other instack 50. This offset allows the undercut receiving structure 56 of thelocking mechanism 32 of the container 54 to align with the undercut 58the locking mechanism 22 of the container 52 in the stack 50.

Turning to FIG. 5 b, a partial section view of the container stack 50 isshown. The stack height C of the stack 50 is reduced because theundercut 58 of the locking mechanism 32 of the container 54 aligns withthe undercut receiving structure 56 of the locking mechanism 22 of thecontainer 52. The depth of undercut receiving structure 56 of thelocking mechanism desirably corresponds with the height of the undercut58 of the locking mechanism. For example, a deeper undercut receivingstructure 56, up to the depth of the undercut 58, reduces the stackheight C by a greater amount, while a shallower undercut receivingstructure 56 reduces the stack height C by a lesser amount. The shape ofthe undercut receiving structure 56 may vary from that depicted in FIG.5 b, so long as the shape of the undercut receiving structure 56 iscapable of stacking on the undercut 58 of the container below it in thestack and of receiving the undercut 58 of the container above it in thestack. Methods of obtaining the offset of the undercut receivingstructure 56 of the locking mechanism 32 of the container 54 relative tothe undercut 58 of the locking mechanism 22 of the container 52 areshown in FIGS. 6 and 7.

FIG. 6 shows a mold base 60 comprising mold cavities 62 a-d forproducing containers. The containers produced by the mold cavities 62a-d are shown to be an approximately square shape. Other shapes arecontemplated, such as rectangular, or polygonal. The mold base 60 is atwo by two mold base because it has two columns and two rows of moldcavities, and may mold four containers at once. Each of the moldcavities 62 a-d is shown with four undercut receiving structures 64 andfour undercuts 66. According to one process, once the containers havebeen molded, they are removed from the mold base 60 and trimmed to theproper shape. The trimmed containers are then stacked. It iscontemplated that the container stack order may be from bottom to top asfollows: the container from the mold cavity 62 a, the mold cavity 62 b,the mold cavity 62 d, and the mold cavity 62 c. Stacking the containersin this order reduces the stack height, because the undercuts 66 of thelocking mechanisms of the containers are aligned with the undercutreceiving structures 68 of the locking mechanisms of the containerdirectly preceding it in the stack. It is contemplated that thecontainers produced by mold cavities 62 a-d of several cycles of moldbase 60 may be stacked in the order described above so that a stack withmore than four containers is produced.

Other stack orders are also contemplated in the present invention. Analternate container stack order may be from bottom to top as follows:the container from the mold cavity 62 a, the mold cavity 62 d, the moldcavity 62 c, and the mold cavity 62 b. This order reduces the stackheight, but the reduction in stack height is not as significant as theprior stacking order. The stack height is not reduced as much in thisstacking order because undercut to undercut contact occurs in the stackof containers.

It is further contemplated that larger mold bases, such as a four by twocavity mold base, or an eight by four cavity mold base may be used inthe current invention. It is also contemplated that a stack ofcontainers would be formed from each column of the mold base 60.According to one process, the order of the first stack of containers maybe from bottom to top as follows: the container from the mold cavity 62a, the mold cavity 62 c. The order of the second stack may be frombottom to top as follows: the container from the mold cavity 62 b themold cavity 62 d. It is contemplated that the containers of severalcycles of mold base 60 may be stacked in this order to produce twostacks with more than two containers per stack. It is furthercontemplated that a non-matrix mold may be used.

The embodiment depicted in FIG. 7 is similar to that depicted in FIG. 6except that the mold base 70 produces containers that have a generallycircular shape in mold cavities 72 a-d. Other shapes are contemplated,such as oval or oblong. The mold base 70 depicted in FIG. 7 is a two bytwo mold base because it has two columns and two rows of mold cavitiesand may mold four containers at once. Each of the mold cavities 72 a-dis shown with three undercut receiving structures 74 and three undercuts76. According to one process, once the containers have been molded, theyare removed from the mold base 70 and trimmed to the proper shape. Thetrimmed containers produced by the mold cavities 72 a-d are thenstacked. It is contemplated that the stack order may be from bottom totop as follows: the container from the mold cavity 72 a, the mold cavity72 c, the mold cavity 72 b, and the mold cavity 72 d. Stacking thecontainers in this order reduces the stack height, because the undercuts76 of the locking mechanisms of the containers are aligned with theundercut receiving structures 78 of the locking mechanism of thecontainer directly preceding it in the stack. It is contemplated thatthe containers of several cycles of mold base 70 would be stacked in theorder described above so that a stack with more than four containers wasproduced.

Other stack orders are also contemplated in the present invention. Usingthe mold 70, an alternate stack order may be from bottom to top asfollows: the container from the mold cavity 72 a, the mold cavity 72 b,the mold cavity 72 c, and the mold cavity 72 d. This order reduces thestack height, but the reduction in stack height is not reduced as muchas the prior stacking order using containers formed from mold 70, asundercut to undercut contact is taking place.

It is further contemplated that larger mold bases, such as a four by twocavity mold base, or an eight by four cavity mold base may be used inthe current invention, or any other matrix mold base may be used. It isalso contemplated that a stack of containers may be formed from eachcolumn of the mold base 70. According to one process, the order of thefirst stack may be from bottom to top as follows: the container from themold cavity 72 a, the mold cavity 72 c. The order of the second stackmay be from bottom to top as follows: the container from the mold cavity72 b, the mold cavity 72 d. It is contemplated that the containers ofseveral cycles of the mold base 70 may be stacked in this order toproduce two stacks with more than two containers per stack. It is alsocontemplated that non-matrix mold base may be used.

Turning now to FIG. 8, a mold base 80 is shown that is capable ofproducing three containers per cycle in mold cavities 82 a-c. Mold base80 is a 1 by 3 mold base because it has one column of mold cavities andthree rows of mold cavities. The mold cavities 82 a-c are identicalexcept that the first cavity 82 a is at a first angle D relative to themold base 80, the second cavity 82 b is at a second angle E relative tothe mold base 80, and the third cavity 82 c is at a third angle Frelative to the mold base 80. The first angle D is from about 80° toabout 100°, the second angle E is from about 50° to about 70°, and thethird angle F is from about 20° to about 40°.

Each of the mold cavities 82 a-c is shown with three undercut receivingstructures 84 and three undercuts 86. According to one process, once thecontainers are molded they are removed from the mold base 80 and trimmedto the proper shape. The trimmed containers are then stacked. It iscontemplated that the stack order may be from bottom to top as follows:the container from the mold cavity 82 a, the mold cavity 82 c, andfinally the mold cavity 82 c. Stacking the containers in this orderreduces the stack height, because the undercuts 86 of the lockingmechanisms of the containers are in alignment with the undercutreceiving structure 88 of the locking mechanism of the containerdirectly preceding it in the stack.

It is contemplated that the containers of several cycles of mold base 80would be stacked in the order described above so that a stack with morethan three containers is produced.

It is further contemplated that larger mold bases, such as a two bythree cavity mold base, or an eight by four cavity mold base may be usedin the current invention. It is also contemplated that a stack ofcontainers would be formed from each column of a multi-column mold base.It is also contemplated that a non-matrix mold base may be used.

It is additionally contemplated that the mold cavities as shown in FIG.8 may have a different shape from the generally round shape depicted.For example, the mold cavities may be generally polygonal. If generallypolygonal mold cavities are employed, the angle of rotation of the moldcavities within the mold base would vary from that described inconnection to FIG. 8. For example, if a generally rectangular moldcavity is employed the angle of rotation between each mold cavities isapproximately one hundred and eighty degrees (180°).

It is additionally contemplated that the methods of using mold bases 70,80 may be combined such that a mold base with mold cavities of varyinggeometry are combined with the rotation of the mold cavities relative tothe mold base to produce a stack of containers with undercuts aligningwith the undercut receiving structures of the preceding container in thestack.

Referring to FIG. 9, a mold base 90 is shown comprising mold cavities 92a-f. The mold base 90 of FIG. 9 is a two by three mold base because ithas two columns of mold cavities and three rows of mold cavities and iscapable of molding six containers at once. Each of the mold cavities 92a-f of the mold base 90 is of an approximately polygonal shape. Each ofthe mold cavities 92 a-f is shown with four undercut receivingstructures 94 and four undercuts 96. According to one process, there aretwo mold cavity designs in mold base 90 of FIG. 9. The mold cavities 92a, 92 c, and 92 e are the first mold cavity design, and mold cavities 92b, 92 d, and 92 f are the second mold cavity design. Once the containershave been molded they are removed from the mold base 90 and trimmed tothe proper shape. The trimmed containers are then stacked. It iscontemplated that the stack order may be from bottom to top as follows:the container from the mold cavity 92 a, the mold cavity 92 b, the moldcavity 92 c, the mold cavity 92 d, the mold cavity 92 e, and the moldcavity 92 f. Stacking the containers in this order will reduce the stackheight, because the undercuts 96 of the locking mechanisms of thecontainers are in alignment with the undercut receiving structures 94 ofthe locking mechanisms of the container directly preceding it in thestack. It is contemplated that the containers produced by mold cavities92 a-f of several cycles of mold base 90 would be stacked in the orderdescribed above so that a stack with more than six containers isproduced.

It is further contemplated that larger mold bases, such as a four by twocavity mold base, or an eight by four cavity mold base may be used inthe current invention. It is also contemplated that a stack ofcontainers would be formed from each column of mold base 90. Accordingto one process, the order of the first stack may be from bottom to topas follows: the container from the mold cavity 92 a, the mold cavity 92b, and the mold cavity 92 c. The order of the second stack may be frombottom to top as follows: the container from the mold cavity 92 d, themold cavity 92 e, and the mold cavity 92 f. It is further contemplatedthat the containers of several cycles of mold base 90 may be stacked inthis order to produce two stacks with more than three containers perstack.

FIG. 10 shows a partial stack 100 of containers produced by a column ofthe mold base 90 of FIG. 9. The stack 100 comprises containers 102-110,the containers are from three cycles of mold base 90. The firstcontainer 102 is from the third cycle of the mold base 90, the second,third, and fourth containers 104,106,108 are from the second cycle ofthe mold base 90, and the fifth container 110 is from the first cycle ofthe mold base 90. The container 102 at the top of the stack, and thecontainer that is second from the bottom of the stack 108 were producedin the third mold cavity 92 c of the mold base 90 of FIG. 9. The secondcontainer from the top 104 of the stack 100 and the bottom container 110of the stack 100 were produced in the first mold cavity 92 a of the moldbase 90 of FIG. 9. The middle container 106 of the stack 100 wereproduced in the second mold cavity 92 b of FIG. 9.

The middle container 106 of the stack 100 is the only container that ismade by a mold cavity with the second mold cavity design in this stack100. Therefore, the undercuts of the locking mechanism of the container104 are in alignment with the undercut receiving structures of thelocking mechanism of the container 106, and the undercuts of the lockingmechanism of the container 106 are in alignment with the undercutreceiving structures of the locking mechanism of the container 108.However, the undercuts of the locking mechanism of the container 102 arein alignment with the undercuts of the locking mechanism of thecontainer 104, and the undercuts of the locking mechanism of thecontainer 108 are in alignment with the undercuts of the lockingmechanism of the container 110. The overall height of stack 100therefore is not truly optimized, as undercut to undercut alignment isoccurring among the locking mechanisms of the containers. However, thisundercut to undercut alignment of the locking mechanisms is unavoidablewhen an odd number of rows of mold cavities are present in a mold base,and the shape of the containers prevents the rotation of the containerswhen forming the stack 100.

This process reduces the stack height of the stack 100, since locationsare present where the undercuts of the locking mechanism of onecontainer are in alignment with the undercut receiving structures of thelocking mechanism of the preceding container. For example, a stackheight H between the second container 104 from the top of the stack 100and the middle container 106 of the stack 100, and between the middlecontainer 106 of the stack 100 and the second container from the bottom108 of the stack 100 is the reduced stack height. A stack height Gbetween the top container 102 and the second container 104 from the topof the stack 100 and between the second container from the bottom 108and the bottom container 110 is the full stack height.

Referring to FIG. 11, a mold base 200 is shown comprising mold cavities210 a,b. The mold base 200 of FIG. 11 is a one by two mold base becauseit has one columns of mold cavities and two rows of mold cavities and iscapable of molding two containers at once. Each of the mold cavities 210a,b of the mold base 200 is of an approximately polygonal shape. Each ofthe mold cavities 210 a,b is shown with four undercut receivingstructures 212 and four undercuts 214. As shown in FIG. 11, each of theundercut receiving structures 212 and each of the undercuts 214 arelocated generally within each of the corners of the containers formed bythe cavities 210 a,b and are at a generally diagonal orientation.According to one process, there are two mold cavity designs in mold base200 of FIG. 11. The mold cavity 210 a is a first mold cavity design, andmold cavity 210 b is a second mold cavity design. Once the containershave been molded they are removed from the mold base 200 and trimmed tothe proper shape. The trimmed containers are then stacked. It iscontemplated that the stack order may be from bottom to top as follows:the container from the mold cavity 210 a, the mold cavity 210 b.Stacking the containers in this order will reduce the stack height,because the undercuts 214 of the locking mechanisms of the containersare in alignment with the undercut receiving structures 212 of thelocking mechanisms of the container directly preceding it in the stack.It is contemplated that the containers produced by mold cavities 210 a,bof several cycles of mold base 200 would be stacked in the orderdescribed above so that a stack with more than two containers isproduced.

It is further contemplated that undercuts and undercut receivingstructures located generally within a corner of a container at agenerally diagonal orientation may vary from that depicted in FIG. 11.For example, it is contemplated that a mold base may contain a firstmold cavity that contains two undercut receiving structures in a firstcorner and a second corner along a first lateral edge, and two undercutsin a third corner and a fourth corner along a second lateral edge,generally opposite the first lateral edge. The mold base contains asecond mold cavity that contains two undercut receiving structures in afifth corner and a sixth corner along a third lateral edge, and twoundercuts in a seventh corner and an eighth corner along a forth lateraledge, generally opposite the third lateral edge. A first container madein the first mold cavity would be stacked with a second container madein the second mold cavity such that the under cut receiving structuresof the second container align with the undercuts of the first container.

It is further contemplated that various methods of reducing the stackingheight of containers may be combined. For example, it is contemplatedthat a mold base may have three mold cavities, wherein the first moldcavity and the second mold cavity have generally identical designs thatare at a different orientation relative to each other, and the thirdmold cavity has a different design.

It is still further contemplated that a mold base may have three moldcavities, wherein the first mold cavity and the second mold cavitieshave a different design, and the third mold cavity has a design that isgenerally identical to the design of the first mold cavity, but thethird mold cavity is rotated within the mold base relative to the firstmold cavity.

The amount of stack height reduction achieved will vary based on thegeometry of the container that is being stacked. According to oneembodiment, the stack height was reduced by about sixty percent (60%).In an embodiment of the present invention where only partial stackheight reduction may be achieved based on the number of mold cavitiesand the mold base cavity geometry the stack may only be reduced by abouttwenty percent (20%).

The reduction in stack height reduces the cube size of thetransportation packaging for a stack of containers. A reduced cube sizefor the transportation packaging reduces the transportation costs fortransporting a stack of containers, as smaller containers are generallymore cost effective to ship than larger containers. A reduction in thecube size for the transportation packaging also lowers the cost ofstoring the containers before the are used, because the smallertransportation packaging occupies less storage space.

The containers of the present invention are typically formed frompolymeric materials, but may be formed from materials such as paper ormetal. The polymeric containers are typically formed from orientatedpolystyrene (OPS), polyethylene terephthalate (PET), polyvinyl chloride(PVC), polyolefins (e.g., polypropylene), and combinations thereof. Itis contemplated that other materials may be used to form the polymericcontainers. The containers may be made from a mineral-filled polymericmaterial such as, for example, talc or calcium carbonate-filledpolyolefin. An example of paper that may be used in forming thecontainers is paperboard or molded fiber. Paperboard and molded fibertypically have a sufficient coefficient of friction to maintain thefirst and second containers in a lockable position.

The materials used in forming the containers may assist in releasablylocking the containers. For example, the material(s) forming thecontainers may have a fairly tacky laminate on one side that correspondswith a fairly tacky laminate on the opposing side, resulting in adesirable releasably lockable container. It is contemplated thatadditives may be added to the containers.

The containers of the present invention are typically made from athermoforming process. However, it is also contemplated that thecontainers may be made using other processes known in the art such as,but not limited to, an injection molding process, a rotomolding process,a rotational molding on a planar surface process, a stamping process, ora molded fiber process.

The containers of the present invention are typically disposable, but itis contemplated that they may be reused at a future time.

As discussed above, the containers may be used with food items. A methodof using such containers includes placing the food and locking thecontainer to form a container with food therein. The container is thenplaced in a heating apparatus and heated. Typical heating apparatusesinclude microwaves and conventional ovens. The containers may containsolid food products. The containers may be used for storage in therefrigerator and/or the freezer.

The thickness of the container generally ranges from about 0.002 toabout 0.25 inch, but is typically from about 0.005 to about 0.04 inch.The containers may be opaque or a variety of colors or colorcombinations. The containers may be transparent if it is desired for thecustomer to ascertain the nature of the accommodated product and thecondition thereof without having to open the container.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

1. A method for forming a reduced-height stack of a plurality ofcontainers comprising: providing a first container having at least afirst undercut and at least one undercut receiving structure, the atleast a first undercut being located at a first position, the at leastone undercut receiving structure being located at a second position;providing a second container having at least a second undercut and atleast one undercut receiving structure, the at least a second undercutbeing located at a third position, the at least one undercut receivingstructure being located at a fourth position, the third position being adifferent location from the first position, the fourth position being adifferent location from the second position, the first and secondcontainers being of generally equal sizes; and arranging the first andsecond containers to form a stack of a plurality of containers, whereinthe at least a first undercut of the first container at the firstposition aligns with and fits within the at least one undercut receivingstructure of the second container at the fourth position so as to reducethe stack height.
 2. The method of claim 1 wherein the first and secondcontainers are made using a forming process.
 3. The method of claim 1wherein the first and second containers are thermoformed.
 4. The methodof claim 1 wherein the first and second containers are injection molded.5. The method of claim 1 wherein the first and second containers arepolymeric containers.
 6. The method of claim 1 wherein the first andsecond containers are made of molded fiber.
 7. The method of claim 1further comprising: providing a plurality of first containers; providinga plurality of second containers; and arranging a plurality oftwo-container stacks, the respective undercuts of the plurality of firstcontainers at the first position being aligned with and fitted withinwith respective undercut receiving structures of the plurality of secondcontainers at the fourth position so as to reduce the stack height.
 8. Amethod for forming a reduced-height stack of containers comprising:providing a mold base comprising at least a first mold cavity having afirst design and a second mold cavity having a second design, the firstand second designs being different; making a first container in thefirst mold cavity, the first container having at least one undercutlocated at a first position and at least one undercut receivingstructure located at a second position; making a second container in thesecond mold cavity, the second container having at least one undercutlocated at a third position and at least one undercut receivingstructure located at a fourth position, the third position being adifferent location from the first position, and the second positionbeing a different location from the fourth position; removing the firstand second containers from the respective first and second moldcavities; and arranging the first and second containers to form atwo-container stack, wherein the at least a first undercut of the firstcontainer at the first position aligns with and fits within the at leastone undercut receiving structure of the second container at the fourthposition so as to reduce the height of the two-container stack.
 9. Themethod of claim 8, wherein the mold base further comprises a third moldcavity having a generally identical design as the first mold cavity, thethird mold cavity being rotated within the mold base relative to thefirst mold cavity; making a third container in the third mold cavity,the third container having at least one undercut located at a fifthposition and at least one undercut receiving structure located at asixth position; removing the third container from the third mold cavity;and arranging the third container with the first and second containersto form a three-container stack, wherein the at least a first undercutof the third container at the fifth position aligns with and fits withinthe at least one undercut receiving structure of the first container atthe second position so as to reduce the height of the three-containerstack.
 10. The method of claim 8, wherein the mold base furthercomprises a third mold cavity and a fourth mold cavity, the moldcavities being arranged in two rows and two columns, the first andsecond mold cavities comprising a first column of mold cavities, thethird and fourth mold cavities comprising a second column of moldcavities, the design of the third mold cavity being different from thedesign of the fourth mold cavity, the method further comprising: makinga third container in the third mold cavity, the third container havingat least one undercut being located at a fifth position and at least oneundercut receiving structure being located at a sixth position; making afourth container in the fourth mold cavity, the fourth container havingat least one undercut being located at a seventh position and at leastone undercut receiving structure being located at an eighth position,the fifth position being a different location from the seventh position;removing the third and fourth containers from the respective third andfourth mold cavities; arranging the third and fourth containers to forma two-container stack, the at least one undercut of the third containerat the fifth position being aligned with and fitted within the at leastone undercut receiving structure of the fourth container at the eighthposition so as to reduce the height of the two-container stack.
 11. Amethod for forming a reduced-height stack of containers comprising:providing a mold base comprising at least a first mold cavity and asecond mold cavity, the design of the first mold cavity beingsubstantially identical to the design of the second mold cavity, thesecond mold cavity being rotated in the mold base relative to the firstmold cavity; making a first container in the first mold cavity, thefirst container having at least one undercut being located at a firstposition and at least one undercut receiving structure being located ata second position; making a second container in the second mold cavity,the second container having at least one undercut being located at athird position and at least one undercut receiving structure beinglocated at a fourth position, the first position being a differentlocation from the third position relative to the mold base; removing thefirst and second containers from the respective first and second moldcavities; and arranging the first and second containers to form atwo-container stack, the at least one undercut at the first position ofthe first container being aligned with and fitted within the undercutreceiving structure at the fourth position of the second container so asto reduce the height of the two-container stack, without furtherrotating the containers after removing the containers from the moldcavities.
 12. The method of claim 11, wherein the mold base furthercomprises a third mold cavity having a design different than the firstmold cavity; making a third container in the third mold cavity, thethird container having at least one undercut located at a fifth positionand at least one undercut receiving structure located at a sixthposition; removing the third container from the third mold cavity; andarranging the third container with the first and second containers toform a three-container stack, wherein the at least a first undercut ofthe third container at the fifth position aligns with and fits withinthe at least one undercut receiving structure of the first container atthe second position so as to reduce the height of the three-containerstack.
 13. The method of claim 11, wherein the mold base furthercomprises a third mold cavity and a fourth mold cavity, the moldcavities being arranged in two rows and two columns, the first andsecond mold cavities comprising a first column of mold cavities, thethird and fourth mold cavities comprising a second column of moldcavities, the design of the third mold cavity being substantiallyidentical to the design of the fourth mold cavity, the method furthercomprising: making a third container in the third mold cavity, the thirdcontainer having at least one undercut being located at a fifth positionand at least one undercut receiving structure being located at a sixthposition; making a fourth container in the fourth mold cavity, thefourth container having at least one undercut being located at a seventhposition and at least one undercut receiving structure being located atan eighth position, the fifth position being a different location fromthe seventh position; removing the third and fourth containers from therespective third and fourth mold cavities; arranging the third andfourth containers to form a second two-container stack, the undercut ofthe third container located at the fifth position being aligned with andfitted within the undercut receiving structure of the fourth containerlocated at the eighth position so as to reduce the height of the secondtwo-container stack, without further rotating the containers afterremoving them from the third and fourth mold cavities.
 14. A stack ofcontainers comprising: a first container comprising a locking mechanismincluding at least one undercut at a first position and at least oneundercut receiving structure at a second position; and a secondcontainer comprising a locking mechanism including at least one undercutat a third position and at least one undercut receiving structure at afourth position, the first and second containers are stacked such thatthe at least one undercut at the first position is aligned with the atleast one undercut receiving structure at the fourth position, and theat least one undercut at the first position contacts the undercutreceiving structure at the fourth position thereby reducing the stackheight.
 15. The stack of containers of claim 14 further comprising athird container, the third container comprising a locking mechanismincluding at least one undercut at a third position and a least oneundercut receiving structure at a fourth position, wherein the thirdcontainer is stacked such that the at least one undercut at the thirdposition is aligned with the at least one undercut receiving structureof the first container at the second position, and the at least oneundercut at the third position contacts the undercut receiving structureat the second position thereby reducing the stack height.
 16. A stack ofcontainers comprising: a first container wherein the first containercomprises a locking mechanism including at least one undercut at a firstposition and at least one undercut receiving structure at a secondposition; and a second container wherein the second container comprisesa locking mechanism including at least one undercut at the firstposition and at least one undercut receiving structure at the secondposition; a third container wherein the third container comprises alocking mechanism including at least one undercut at a third positionand at least one undercut receiving structure at a fourth position; afourth container wherein the fourth container comprises a lockingmechanism including at least one undercut at the first position and atleast one undercut receiving structure at the second position; and afifth container wherein the fifth container comprises a lockingmechanism including at least one undercut at the first position and atleast one undercut receiving structure at the second position, whereinthe second container is aligned such that the at least one undercut atthe first position is aligned with the at least one undercut at thefirst position of the first container, the third container is alignedsuch that the at least one undercut at the third positioned is alignedwith and fitted within the at least one undercut receiving structure atthe second position of the second container, the fourth container isaligned such that the at least one undercut at the first position of thefourth container is aligned with and fitted within the at least oneundercut receiving structure at the fourth position of the thirdcontainer, and the fifth container is aligned such that the at least oneundercut at the first position of the fifth container is aligned withthe at least one undercut at the first position of the fourth container,such the stack height between the second, third, and fourth containersis minimized and the overall stack height is reduced.